According to one of the guides on Commerce Clearinghouse:
Causation
"A qualifying event will not occur upon a loss of coverage under a group health plan unless the loss of coverage is linked directly to one of the events listed in
COBRA"
This would mean that him dropping her is not a qualifying event.
"The issue of causation also may arise in the case of a divorce. For example, it may happen that an employee cancels his or her spouse's health coverage as of a date that is before the date that the divorce becomes final.156 In such a case, the spouse's loss of coverage is not due to a
COBRA qualifying event (i.e., divorce). However, pursuant to the IRS's final
COBRA regulations, the "anticipatory cutback" rule may apply, and, thus, the spouse may be entitled to prospective
COBRA coverage. (See section 5.04[E].)"
5.04[E] says: Anticipatory Cutbacks
"The IRS takes the position that if an employer reduces or eliminates group health plan coverage in anticipation of one of the events listed in
COBRA (a course of action referred to as an anticipatory cutback), the cutback in coverage will be disregarded, and the issue of whether a loss of coverage has occurred will be determined by examining the pre-cutback level of benefits."
Therefore, if he is planning on getting a divorce, and this was in anticipation of it, then she might still be eligible for
COBRA.